Thomas of Lancaster, 1st Duke of Clarence, KG (1387 – 22 March 1421), was the second son of King Henry IV of England and his first wife, Mary de Bohun. After the death of his father he participated in the military campaigns of his brother King Henry V.

Heir to the thone in the event of his brother's death, he was left in charge of English forces when Henry returned temporarily to England after his marriage to Catherine of Valois. He led the English in their disastrous defeat at the hands of a mainly Scottish force coming to the aid of the French, at the Battle of Baugé. In a rash attack he and his leading knights were surrounded and Thomas was killed.

After his father became ill in 1411, his older brother became head of the royal council. Conflicts arose between the young Henry and his father when the prince gathered a group of supporters favouring his policy of declaring war on France. The prince was removed from the council by his father after he had defied the king's wishes by persuading it to declare war. Thomas was given his brother's seat, and fell in line with his father's peace policy.[2]

During the wars of his elder brother Henry V in France, Clarence fought in the Siege of Rouen (July 1418 – 19 January 1419), where he commanded the besieging force. After Henry had negotiated the Treaty of Troyes, in which he became heir to the French throne, the king returned to England with his new wife Catherine. The Dauphin, the disinherited former heir, refused to accept the situation and organised continuing resistance, aided by a Scottish army led by John Stewart, Earl of Buchan.

Following the King's instructions, Clarence led 4000 men in raids through the Anjou and Maine.[3] This chevauchée met with little resistance, and by Good Friday, 21 March 1421, the English army had made camp near the little town of Vieil-Baugé. The Franco-Scots army of about 5000 also arrived in the Vieil-Baugé area to block the English army's progress; it was commanded by the Earl of Buchan and the new Constable of France, the Sieur de Lafayette; however, the English forces were dispersed, and, significantly, many of the English archers had ridden off in search of plunder or forage. On Easter Saturday, one of these foraging groups captured a Scots man-at-arms who they brought before the Duke of Clarence. Clarence was keen to engage the enemy; however, he had a problem: the following day was Easter Sunday, one of the most holy days in the Christian calendar, when a battle would be unthinkable. A two-day delay was also deemed as out of the question.[4][5] According to the chronicles of Walter Bower both commanders agreed a brief truce to celebrate Easter, but then joined battle that day.[6]

Perhaps underestimating the size of the Franco-Scottish army, Clarence decided to launch a surprise cavalry-led attack rather than use his archers against the enemy. With only about 1500 men-at-arms available, and virtually no archers, he charged the Franco-Scottish lines. The shock temporarily disordered the Franco-Scots, but soon Clarence and his knights were overwhelmed. Clarence was unhorsed by a Scottish knight and finished off on the ground by Sir Alexander Buchanan, probably with a mace.[7][4]

His natural son John accompanied the remains of his father from Baugé to Canterbury for their interment. This Sir John Clarence had a grant of lands in Ireland from Henry V and was buried in Canterbury Cathedral. The noble de Langlée family of France claimed him for their ultimate ancestor. Henry V was forced to return to France with a new army to retrieve the situation.

His executors, as seen in a legal record of 1430, were John Colvylle, of Neuton, Cambs, knight; Henry Merston, of Westminster, clerk & his widow, Margaret, Duchess of Clarence, living in Bermondsey, Surrey. [8]